The present invention relates generally to boiler control systems and more specifically to a boiler control system for use with only one boiler or with multiple boilers. The present invention relates specifically to a Boiler Interface Controller, a Human Interface Panel and a Fault Tolerant Multiple Boiler Sequencer. The system will be explained with reference to hot water boiler(s) but it is understood that it applies as well to water heater(s).
The application of a thermostat to boiler control has traditionally been handled by an electromechanical control that presents a digital (on or off) request for heat to a flame safety controller that would actuate a gas valve and purge system on a typical gas boiler. With the advent of microprocessor-based controls, many new features allow display and control of thermostat information, e.g., setpoint information and control point status on an annunciator screen.
Flame safety boiler controls directly affect those elements that may cause an unsafe condition. Flame safety controls have very high safety standards and require strict testing and failure analysis, particularly for microprocessor-based controls. This level of safety and control can demand extra dollar value in the market place due to the liability issues and the difficulty of implementing controls that meet these safety standards. Customization and feature enhancements of flame safety controllers are prohibitively expensive, due to the cost of certification and testing. Components of the gas flame safety controller ignition cycle include safety checks, pre-purge, igniter surface preparation, trial for ignition, gas valve actuation, ignition, and post-purge. Manufacturers of flame safety products typically provide flame safety controllers to an original equipment manufacturer (OEM) for boilers. The OEM then integrates these controls into their boiler designs. Some of the boiler control products also incorporate temperature control sensing and setpoints into the device, but these are usually limited to single standalone boiler devices.
Smaller boilers can be designed to be xe2x80x9ccondensingxe2x80x9d; meaning the efficiency will be much higher than a traditional boiler design. These condensing designs typically require a feedback loop of hot water to ensure that the water temperature to the main heat exchanger does not go below the condensing temperature of the waste combustion gas, typically 130 degrees F. In the past this feedback loop normally included a manually controlled valve.
New gas valve technologies have evolved that will automatically adjust the boiler combustion air to fuel ratio based on the air pressure of firing rate combustion rate. With the new gas valve technologies, the addition of a variable frequency drive (VFD) allows for xe2x80x9cmodulatingxe2x80x9d or controlling the firing rate of the boilers from low to high firing rate. In addition, VFD allows purging of the combustion chamber when gas is not intended to be present.
Thus a need exists for a low-cost high-performance Boiler Interface Controller (BIC) that interfaces with a Flame Safety Controller and other boiler devices to provide the benefits of digital boiler control and includes control of a bypass valve in a condensing boiler, control of variable firing rate and greatly increased information on the operation of the boiler.
The present invention also relates to a Human Interface Panel (HIP) for use with a Boiler Interface Controller (BIC) that may be used with systems having only one boiler or having multiple boilers. The HIP will first be described for use with a BIC, but it is to be understood that the HIP of the present invention is also useful with any boiler that is arranged as described herein.
In the past human interface devices have typically been related to just one aspect independent of others, e.g., such individual aspects could include flame safety, thermostat, gas valve, bypass control, sequencer, and maintenance. There has been no integration of these aspects in previous interfaces. In addition, past displays require expensive and numerous remote interfaces, relays and complicated electrical communication protocols that require highly specialized, flame-safety-robust, fail safe communications protocols. This was necessary because an improper electrical connection or short in a flame safety controller interface could shut down or disable a crucial flame control activity. Thus a high cost interface with substantial safeties and electrical protections was required.
Boiler controls require that a number of sequential events occur before the controlled ignition of gas in the boiler occurs. Examples of these events include but are not limited to proof of water flow, proof of satisfactory gas pressure, and proof of combustion fan operation. If any of these and other events fail to be proven, then the sequence of events that normally leads to controlled ignition is halted and the cause of the failure must be investigated and corrected. In the past when this occurs the only known fact is likely to be that the boiler is not functioning and this may only become known after the occupied space served by the boiler is no longer heated to a comfort condition. Typically a boiler service person would then be called and would eventually inspect the boiler and through trained observation and/or a series of tests identify the problem and do what is necessary to correct the problem. This process may result in considerable period during which the space served by the boiler is not heated to a comfort condition. An uncomfortable occupied space can result in dissatisfied tenants and/or a considerable loss of productivity. In addition to the scenario just described there are needs for regular inspection and servicing of boilers under circumstances where the boiler has not failed. Boilers are complicated devices that should be periodically inspected and the necessary sequential events that lead to controlled ignition of gas should be observed by a qualified boiler service person to determine that they are properly functioning. Testing or diagnostic tools that enable the service person to observe the sequential events will help to assure that the boiler is functioning properly. Thus a need exists for a device that allows a person to better understand the functions that are occurring or not occurring within the boiler control system.
The present invention also relates to a Fault-tolerant Multi-Node stage Sequencer. The design of boiler systems for commercial, industrial, and institutional buildings is typically performed by a consulting engineer, who specifies the type, number, and size of boilers needed for heating systems. There are many factors that weigh into the decisions an engineer makes when selecting and sizing boilers for a heating system including capacity of the system, what is the load present on the system, and what is the worst case load conditions that would be required for the system to provide adequate heat. The specification of a single, large heating capacity boiler can satisfy the heating demand for the worst load conditions, which in cold climate Heating Ventilating and Air Conditioning (HVAC) applications would be defined as the xe2x80x9cdesign temperaturexe2x80x9d. Typically, a very cold outside air temperature requires the full capacity of the boiler to provide heat for the building. However, the typical use of this load level would be limited to a total of less than 2% of the total year time. Design of smaller, but multiple boiler system can lead to a reduction of the xe2x80x9cexcess capacityxe2x80x9d of the boiler system on a typical system from 40% to 4%, which represents significant operational savings, increased system efficiency, and improved heat system reliability. For example a lightly loaded system could have its requirements met by using only 1 of 3 smaller, more efficient boilers instead of using ⅓ the capacity of a larger boiler.
The control system for a multiple boiler or staged boiler system is necessarily different than the control system for a single boiler. For example, in a multiple boiler system, consideration must be given to the number of stages, whether the boilers have variable firing rates, under what conditions an individual boiler will be turned on or turned off, the strategy for equalizing run time of the individual boilers, what occurs in the event of the failure of an individual boiler and other factors. In the past these considerations have frequently required a more or less custom design and installation process and the increased costs that accompany such a process. Thus there is a need for a boiler control system that takes into consideration the number of boiler stages and whether the boilers have a variable firing rate, provides a technique for decisions as to adding or deleting a boiler, equalizes run times and automatically compensates in the event of failure of an individual boiler.
The present invention solves these and other needs by providing in a first aspect a method for operating a boiler including sensing a demand for heat and generating and ignition request to a flame safety controller. A first evaluation mode in a succession of evaluation modes then sets certain defined conditions, reads certain defined conditions and compares selected conditions. If the comparison indicates normal operation, then a next evaluation mode occurs. The boiler control system transitions to a failure mode if an evaluation mode is not successfully completed. In another aspect the boiler control system provides a signal for controlling a variable firing rate boiler
In another aspect the HIP of the present invention solves these and other needs by providing a method of analyzing information from a boiler control system. The method includes providing a series of status modes with each status mode being represented as an input condition to be tested. A relative priority structure is established among the status modes and a unique message is associated with each said status mode having an input condition that is true. The individual status modes are then tested in an order defined by the priority structure until a status mode in a true condition is found. The unique message associated with the status mode found to be true is then provided on an electronic display. The status modes may be selected from one or more of diagnostic modes, start up modes emergency modes and stage information modes.
In yet another aspect, the Sequencer of the present invention provides a method for controlling energy systems such as multiple boiler systems to meet an energy need. A controller is configured as a sequencer and the remaining controllers act as individual boiler controllers. The energy need is determined by measurements at the sequencer. Individual boiler controllers periodically send status messages to the sequencer and a record of runtimes of the boilers is maintained at the sequencer. The sequencer periodically sends control commands to the boiler controllers to add or delete boilers. The control commands give consideration to the runtimes of the boilers.